1. Field of the invention
This invention relates to an apparatus for the formation of images in which a photosensitive sheet coated with pressure-rupturable capsules containing chromogenic materials is first exposed to light at a light-exposure section to obtain a latent image and then is brought together with an image-receiving sheet coated with developing materials at a pressure-transfer section to be pressurized, thereby allowing the chromogenic materials to react with the developing materials to obtain a colored image on the image-receiving sheet, and more particularly relates to an apparatus for the formation of images in which the portion of the photosensitive sheet that has passed through the light-exposure section temporarily stays at a buffer section before being transported into the pressure-transfer section.
2. Description of the prior art
An apparatus for the formation of images in which a photosensitive sheet coated with pressure-rupturable capsules containing chromogenic materials is first exposed to light to obtain a latent image and then is pressed against an image-receiving sheet coated with a developing materials to obtain a colored image on the image-receiving sheet has been proposed by, for example, Japanese Laid-Open Patent Publication No. 58-88739.
The image-forming process in such an apparatus comprises two steps; a light-exposure step and a pressure-transfer step. In the light-exposure step, the photosensitive sheet, one side of which is coated with pressure-rupturable capsules containing chromogenic materials that are hardened when exposed to light, is first transported into a light-exposure section, where it is exposed to light reflected from an original. The light reflected from the original selectively illuminates the pressure-rupturable capsules on the photosensitive sheet so that some of the capsules receive the light and become hardened, while others do not receive the light and are left unchanged, resulting in a latent image corresponding to the image of the original. Then, in the pressure-transfer step, the photosensitive sheet on which the latent image has been formed is transported into the pressure-transfer section, where the photosensitive sheet is placed together with the image-receiving sheet and pressure is applied thereto. Thus, the pressure-rupturable capsules that have not been hardened rupture, allowing the chromogenic materials contained therein to flow out onto the image-receiving sheet. Then, the chromogenic materials react with the developing materials coated on the image-receiving sheet, which gives rise to color in the chromogenic materials, resulting in a colored image corresponding to the latent image on the image-receiving sheet. In general, the pressure-transfer section consists of a pair of pressure rollers, between which the photosensitive sheet and the image-receiving sheet are supplied at the same time to be pressurized.
In the light-exposure step mentioned above, the speed at which the photosensitive sheet is transported through the light-exposure section determines the light-exposure time, which influences the quality of a latent image to be formed on the photosensitive sheet. Similarly, in the pressure-transfer step mentioned above, the speed at which the photosensitive sheet is transported through the pressure-transfer section determines the time of the reaction between the chromogenic materials and the developing materials. The reaction time influences the quality of a colored image to be formed on the image-receiving sheet. In order to obtain a distinct colored image, the photosensitive sheet should be transported through the light-exposure section at the optimum speed (hereinafter referred to as "the optimum light-exposure speed") so that a latent image can be properly formed with the optimum light-exposure time, and then should be transported through the pressure-transfer section at the optimum speed (hereinafter referred to as "the optimum pressure-transfer speed") so that a colored image can be properly formed with the optimum reaction time. In general, the optimum light-exposure speed is different from the optimum pressure-transfer speed. If the photosensitive sheet is continuously transported through the light-exposure section and the pressure-transfer section, it can only be transported at the same speed through those two sections. Thus, the sheet-transporting speed cannot be set at the respective optimum level for each section.
To solve the above-mentioned problem, an apparatus for the formation of images has been proposed by, for example, Japanese Patent Application No. 63-64426 in which the photosensitive sheet is first transported from the roll of the sheet through the light-exposure section to a buffer section at the optimum light-exposure speed and temporarily stays at the buffer section between the light-exposure section and the pressure-transfer section, and is finally transported from the buffer section into the pressure-transfer section at the optimum pressure-transfer speed.
In such an apparatus, the sheet-transportation speed can be set at respective optimum levels for the light-exposure section and the pressure-transfer section, as mentioned above. This makes it possible to properly form a latent image on the photosensitive sheet and a distinct colored image on the image-receiving sheet.
The photosensitive sheet, however, has non-image areas between image-forming areas on which latent images are to be formed. As mentioned above, the pressure-rupturable capsules on the image-forming areas are exposed to light reflected from an original at the light-exposure section so that a considerable number of them are hardened to obtain a latent image. On the other hand, the pressure-rupturable capsules on the non-image areas are not exposed to light at the light-exposure section, so that none of them are hardened. When those unhardened capsules on the non-image areas are transported into the pressure-transfer section, they are pressurized to rupture so that the chromogenic materials flow out onto the pressure rollers or other components within the body of the apparatus, causing the pressure rollers and/or the inside of the body of the apparatus to be stained with the chromogenic materials. This interferes with the smooth operation of the whole apparatus. Moreover, since the image-forming areas have a large number of hardened capsules while the non-image areas have no hardened capsules, the rigidity of the image-forming areas are far greater than that of the non-image areas, and the surface of the non-image areas is far smoother than that of the image-forming areas. This difference in rigidity and smoothness between the image-forming areas and the non-image areas prevents the photosensitive sheet from being smoothly transported, causing the sheet to be crumpled. This may cause the whole apparatus to be jammed by the photosensitive sheet.
One way to solve the above-mentioned problem is to illuminate the non-image areas with use of a lamp or the like. It is, however, difficult to accurately direct the light to the area between the back end of one image-forming area and the front end of the next image-forming area while the photosensitive sheet is being transported. The light cannot be directed onto the non-image area without interfering with the image-forming areas adjacent thereto. If the transportation of the photosensitive sheet is suspended so that the light is accurately directed to the non-image area, the time required for the formation of images increases, which prevents the high-speed operation of the whole apparatus.